Esprit 120 part 2

[Ken82]

Its been a while now since i posted my preliminarily preview of the Esprit 120 mostly due to a  combination of work/family/bad weather and Xmas parties. On Friday evening the forecast was clear until around 7ish so i was able to get a few shots of M45. I chose M45 as its a great star cluster which would be good to determine star shapes in the corner of my sensor.

I was able to get 26x2.5min before the clouds started to roll in. For this test the position of M45 wasn't great so there is a light pollution gradient etc, which isn't important to determining star shapes, optical errors.

Anyway looking at my RAW images id say the scope covers about 98% of the sensor. For the remaining 2% a very small amount of vignetting is visible with a strong histogram stretch and an ever so slight amount of coma on stars at the extremities of the image. If your using a 36mm sensor like me then a very slight crop is necessary, although most people would do this anyway.  If your using a standard APS-C Dslr then your stars are pinpoints to the edge! Very impressive in my book. Zooming into a bright star i can see no signs of star bloating. 

I don't know how Skywatcher are able to achieve such high quality for such a low price (in comparison to high end competitors) but im delighted!

The image ive posted is about 75% crop, for your perusal if anyone wants a full uncropped image please let me know.

 

 

 

[souls33k3r]

Great image Ken. 

One question though, what's with the diffraction spikes/X like thing going on in the bright stars?

[Ken82]

10 minutes ago, souls33k3r said:

Great image Ken. 

One question though, what's with the diffraction spikes/X like thing going on in the bright stars?

Yea interesting, ive noticed the exact opposite diffraction spike on a takahashi i use. Not sure if that's down to the sensor size/lens cell or camera design itself. If i use another (smaller) camera/sensor on the tak  then i dont get the diffraction.

[Craney]

I get diffraction spikes with my Equinox 80.  ( subtle, but definitely 4 way pointed ones) .  If I don't process for a while and do not organise the naming of my raw files I can be left wondering which scope I actually used, as my 6"F4 newt + CC, comes in close with the FL...... and it produces spikes aplenty.

I put it down to the amazing sensitivity of the Atik 414 mono camera.  Probably something in the optical train acts as the source of a 'star' shaped pattern, and the camera just picks it up better than say, my DSLR. 

[ollypenrice]

On 09/12/2018 at 00:55, souls33k3r said:

Great image Ken. 

One question though, what's with the diffraction spikes/X like thing going on in the bright stars?

You've got me worried now! I can hardly see anything which fits this description...

Very bright stars throw up artefacts in most refractors, indeed in most telescopes. In the scheme of things I'd call these very clean. Takahashis throw up their signature 'inverse lighthouse beams,' for instance.

Another source can be the microlenses on some chips. Nothing to do with the scope.

Olly

[Jkulin]

I've seen something similar reported elsewhere with a scratched CCD cover and my mate had similar on his camera, might worth having a look.

[tomato]

Here is Alnitak through an Altair 102 APO, I think there are some 90 degree inverse lighthouse beams going on with this one.